Waterwheels have been known since antiquity and have served principally for generating mechanical power. With the widespread introduction of commercial plants, in particular for generating electricity, water turbines have largely displaced the waterwheel. Consequently, the efforts devoted in the past decades to further technical development and improvement of the performance of waterwheels have been correspondingly small.
Whereas by definition, waterwheels gain mechanical energy from the potential energy of the water, in waterwheel turbines the potential energy as well as, to a usable degree, the kinetic energy of the flowing water is exploited in appropriately formed buckets, or cell walls. Within the class of turbomachinery, the waterwheel turbine is categorized as an impulse turbine.
Providing an overview of the present status of this technology is the book: Bau von Wasserkraftanlagen by Konig/Jehle, published by C. F. Muiller Verlag, third completely revised edition, 1997, containing planning documents for practical applications. Starting on Page 197, one chapter deals with waterwheels. It describes their advantages over turbines, such as comparatively straightforward subsurface works and low-cost, cut-and-cover construction techniques. At the same time, the descriptions of examples of constructed plants present, as a generally accepted disadvantage inherent to this class of devices, the premature outflow of more or less significant water volumes from the amount originally entering each cell, before it attains its submerged level.
The usual graphical representation of the efficiency, .eta., of a waterwheel as a function of the quotient, Q.sub.n /Q, where Q.sub.n is the normal rated flow and Q the actual flow, makes this clear, as in this the maximum efficiency is always less than unity (100%), and remains unchanged over wide variations of the degree of filling of the cells.
In the past, there has been no lack of proposals for improving the cell geometry of waterwheels, or waterwheel turbines, in particular with designs for minimizing water loss from a cell before it has fully traversed the water head. These were concentrated on a projection of the discharge lip of the cell opening, as well as on cell designs for which the virtual center of gravity of the water filling the cell attains a level which is as low as possible beneath that of the inflow and discharge opening. But in this connection, it is known to the specialist that as the length of a cell increases in the radial direction, the directly usable head between the headrace and the tailrace is reduced by an amount approximately double this cell dimension. Hence, increasing this dimension at the cost of only partially filled cells always represents a disadvantageous compromise referred to the theoretically exploitable water energy.
DE 3621312 A1 describes, for example, a waterwheel whose cup-shaped cells are so formed that the tongue projecting far from a cell wall according to invention, prevents the cups emptying too early.
For the task of better exploiting minor water reserves with low volumetric flow and low head, DE 3938748 C2 proposes a solution in which premature discharge of water from a cell is prevented by a pneumatic sealing system for the cells, In this, sealing of the open cells against stationary external boundaries and walls is by means of sealing rings to which pneumatic pressure is applied. The disadvantage of this solution is that any type of sliding seal gives rise to substantial frictional losses, and therefore reductions in efficiency and also involves wear. A waterwheel turbine in accordance with the generic term of claim 1 is known from U.S. Pat. No. 4,385,497.
The purpose of this invention is therefore, by specially designing the cells of waterwheels, or rather of waterwheel turbines, to increase their efficiency in comparison with known designs, referred to the actual water inflow rate to the plant per unit of time and the actual available head. Alternatively formulated, the task is to fill the cells with the water directed to them by way of a channel rapidly, without appreciable water losses and with a high degree of filling, and to exploit the potential of the filled water mass over an effective height approaching that of the water head to generate torque and transmit energy via the wheel shaft better than in known systems. Apart from the water's potential energy, its impulse energy from filling and emptying the individual cells, which is always exploitable in the case of flowing waters without the need for special measures, is to be effectively converted to torque.